This invention relates to refrigeration and more particularly to a sealing arrangement for a rectilinear reciprocable piston of a cryogenic refrigerator.
In many cryogenic refrigerators (i.e., the Stirling, Gifford-MacMahon, and Claude type refrigerators), a piston rectilinearly reciprocates within a cylinder to moveably define a variable volume expansion chamber. A refrigeration gas flows into and out of the variable volume expansion chamber in accordance with the movement of the piston and is cooled by controlled cycling with suitable heat exchange.
A problem associated with these refrigerators is ineffective sealing between the rectilinear reciprocable piston and the cylinder within which it moves. When the sealing is ineffective, the refrigeration gas from the expansion chamber escapes along the piston thus decreasing the efficiency of the refrigerator.
Additionally, ineffective sealing permits the entrance of contaminants (i.e., atmospheric gases such as oxygen, nitrogen, and hydrogen). The problem of contamination becomes especially acute when these refrigerators are employed to cool helium to a liquified state. Helium has an extremly low boiling point remaining in a gaseous state long after most gases have liquified. Therefore, any entering contaminating gas would liquify and seep to the expansion chamber which would further decrease the efficiency of the refrigerator.